Shared Values: The Judo Throw of Argument
The atheists I know love to bring up issues like religion and politics that touch on the very roots of common world-views. The problem we know about, however, is that these issues immediately cause people to get defensive and arguing with them will often reinforce their beliefs. The weight, accuracy, or validity of your argument or beliefs becomes completely irrelevant to your opponent (or those in the audience). Those of us who believe in rational discourse can be discouraged by the kind of polarization documented in the sociological, psychological, and political sciences. In the face of this knowledge, some people reach exclusively to accommodation tactics in order to achieve their ends, but confrontational tactics can find hope by laying a foundation on shared values.
Because reality can be an unforgiving place, many popular ideas tend to have something right, even though some may only be correct "by accident" or misattribution. Anecdotally, I've found that most deconverted atheists still have most of the same fundamental values that were stressed during their religious upbringing. In fact, I think a lot of these values are what cause many people to change their beliefs.
There are many goods that come about when you start a conversation emphasizing shared values. You're overcoming any in-group/out-group distinction (demonization) when you can show your overlapping humanity. This gives you worth, and you are now able to introduce ideas on a level playing field. Even if your arguments fail, you've succeeded in breaking their demonization of the out-group, and this alone may cause doubts in some extremely conservative religious contexts. However, if you're talented enough with your argument, you can even leverage the shared values against the very foundations of their world view.
Not every one of these shared values are going to exist, and sometimes only lip-service is paid to them. But their existence in the world-view you're arguing with is more than sufficient, even if they're not always observed. Please don't use these shared values if you don't actually share them, but feel free to find your own.
Honesty You're honestly stating what your opinions are. Avoid any hints that you're playing games. If you actually are playing games, then don't. It doesn't help. If the only person you care about in the argument is yourself, you're just masturbating in front of them and that's just impolite.
Willingness to stand up for principles Being an out atheist or an out non-Christian, you're doing something that is socially expensive. There is a cost to openly stating your beliefs, and you've probably had to account for these and be prepared for them eventually happening. Lots of religious folks also encounter costs for publicly declaring their beliefs (though most mainstream faiths do not). There is even a small subset of Christians who go to sleep pondering whether they'd take a bullet in a school shooting to declare their love for God/Jesus. You'll get major props for demonstrating your willingness to pay for being open.
Respect for the beliefs Many people call themselves Christians because they still identify with some of the traditions. You've forsaken this label out of respect for the set of beliefs and have forsaken cherry-picking while retaining the label (though you can still cherry-pick verses that you find that you like...for instance, Job is one of my favorite books).
Intellectual consistency and intellectual honesty The inspiration and/or inerrancy of the Bible often lays on some type of test for intellectual consistency. By establishing this, you can often remove ANY arguments from consequence.
Literal interpretations of the Bible One of the easiest ways to achieve intellectual consistency is to try to literally interpret the Bible. If you grant this premise, you can try to wedge them into a corner where they have to admit that to solve even these "apparent contradictions", they have to appeal to their intrinsic moral sense (this argument works better with non-literal interpretations as below). You can also just mire them in really difficult passages to reconcile where you can challenge them on the shared moral value of intellectual consistency.
Non-literal interpretations of the Bible This is one of the areas where I like to have the most fun. The moderate and liberal Christians are extremely slippery (even the conservative Christians think so...another potential shared value?). I've been convinced that the Bible is the "wrong kind of book" to be taken literally, through a historic argument that the notion of Biblical inerrancy with understanding by all the laity is a very recent American tradition going back only a couple hundred years. Non-literalists must concede that reason and their intrinsic moral sense is the filter they apply to the miserable verses that they avoid or the reformation of the tradition they claim as the authority for their dogma. When I have show that I share this moral sense, I can then remove the Bible safely and show a rich humanistic tradition that is unfettered by bronze-age books and can more quickly and humanely help us with deep ethical problems.
There are many more shared values. If you used to be religious, just spend some time thinking about what has and has not changed in your life. If you never were religious, I think having some honest conversations with religious people will help you find common ground...though you'll have to sit through statements that may make your head explode, so please don't hold me morally responsible for that.
Shared values are also stepping stones to move from one world view to another. By standing on these shared values, you can show that there is something solid on which they can stand while they re-evaluate their life in search of truth, and because you also stand on these shared world-views they feel safe standing with you. Questions of transcendental purpose and meaning, transcendental morality, transcendental truth, and other arguments can be evaluated with a safety net of objective moralities and objective truth (even if it may be only approximated through discovery), and a journey of creating your own meaning and purpose. Rather than a blanket conversion, your goal should be for the people you argue with to refine their own beliefs through the fires of rational discourse. When you can remove a lot of these fears, more people are willing to temporarily occupy your beliefs and "try them on" to see if the world makes more sense.
I'd love to hear comments and criticism on this topic from all sides.